As is the case under U.S. patent law, Taiwan's patent system also allows patent claims to be drafted in means-plus-function or step-plus-function language. Article 18, Paragraph 8 of the Enforcement Rules of the Patent Act, amended on July 1, 2004, stipulates that "A technical feature in a patent claim for an invention which consists of a combination of multiple technical features may be expressed in means-plus-function or step-plus-function language. Such claim shall be interpreted to cover the corresponding structure, material, or acts described in the description and equivalents thereof." The provision was also adopted in Article 19, Paragraph of the current Enforcement Rules of the Patent Act, as amended and promulgated on November 9, 2012, and implemented on January 1, 2013.

The aforementioned provision under the Enforcement Rules of the Patent Act has led to the following legal controversial question in patent litigation: For a patent drafted with means-plus-function or step-plus-function claims, if the corresponding structures, materials or acts are not found in the patent specification, would the patent be deemed to have failed to meet the "definiteness and clarity" requirement under Article 26 of the Patent Act, which reads, "the description shall fully disclose the invention in a manner clear and sufficient for it to be understood and carried out by a person ordinarily skilled in the art"? The Intellectual Property Court has expressed various views.

The Intellectual Property Court expressed an affirmative opinion in its 2009 Civil Judgment Min-Zhuan-Shang-Zi No. 19 rendered in January 2010. Claim 6 of the patent at issue was related to an invention of computer software and drafted in means-plus-function language. The Intellectual Property Court ruled that the claim failed to meet the definiteness and clarity requirement on the grounds that the corresponding structures, materials or acts were not found in the patent specification. In spite of the Supreme Court's 2011 Judgment Tai-Shang-Zi No. 480, which reversed and remanded the aforesaid judgment, the Intellectual Property Court upheld its initial view in 2011 Judgment Min-Zhuan-Shang-Geng(1)-Zi No. 5 dated October 2011. The case was remanded again by the Supreme Court with 2012 Judgment Tai-Shang-Zi No. 1673, but the Intellectual Property Court ruled again for the same reasons in 2012 Judgment Min-Zhuan-Shang-Geng(2)-Zi No. 5 dated June 2013 that Claim 6 of said patent lacked definiteness and clarity.

Meanwhile, the Intellectual Property Court expressed a negative opinion regarding the abovementioned legal issue in 2012 Administrative Judgment Xing-Zhuan-Su-Zi No. 28 dated January 2013. The Plaintiff claimed that said patent failed to meet the definiteness and clarity requirement on the grounds that its claims were drafted in means-plus-function language but there were no descriptions about the corresponding structures, materials or acts found in the patent specification. The Intellectual Property Court judgment states: While Article 18, Paragraph 8 of the Enforcement Rules of the Patent Act stipulates that such claim drafted in means-plus-function or step-plus-function language shall be interpreted to cover the corresponding structure, material, or acts described in the description and equivalents thereof, this does not mean that the description of the patent specification is required to contain the structures, materials or acts or equivalents of said claim to meet the definiteness and disclosure requirements under the Patent Act. The definiteness requirement shall be determined by whether a claim may be understood by a person ordinarily skilled in the art. The view was upheld by Supreme Administrative Court 2013 Judgment Pan-Zi No. 355 dated June 2013.

Nevertheless, the Intellectual Property Court expressed an affirmative opinion regarding the preceding legal issue in 2014 Judgment Xing-Zhuan-Su-Zi No. 70 dated January 2015. The court ruled that claims in said patent application were drafted in means-plus-function language but the patent specification did not specify the structures, materials or acts of the function, and thus failed to meet the definiteness requirement. An appeal was filed by the patent applicant, whereupon the Supreme Administrative Court delivered 2016 Judgment Pan-Zi No. 149 in June 2016 and reversed the original ruling.

The Supreme Administrative Court stated in the above 2016 Judgment Pan-Zi No. 149 that "the Patent Act explicitly lists all reasons for rejection of patent applications, and therefore a patent application cannot be rejected solely on the grounds of the Enforcement Rules of the Patent Act or the Patent Examination Guidelines." Detailed reasons for expressing a negative opinion regarding the preceding legal issue were given as follows:

Article 19, Paragraph 4 of the existing Enforcement Rules of the Patent Act states only that claims drafted in means-plus-function or step-plus-function language shall be interpreted, "if needed," to cover the corresponding structure, material, or acts described in the description and equivalents thereof. The Patent Act does not require a patent applicant to describe the corresponding structures or acts in the specification, neither does it provide that the patent specification shall contain descriptions of the structures, materials or acts corresponding to the means-plus-function claims to meet the definiteness requirement under the Patent Act. Hence, the laws supplemented by Article 19, Paragraph 4 of the Enforcement Rules of the Patent Act are those related to the interpretation of patent claims, and said article aims only to establish the boundaries for the protection scope of the patent, not to define or explain the definiteness and clarity requirement. Whether a claim meets the definiteness and clarity requirement should be determined by the purpose of means-plus-function claims and the criteria provided by the Patent Act.

Based on the rulings above, the Supreme Administrative Court appears to have adopted a negative position on this legal issue. In other words, means-plus-function claims cannot be deemed to have failed to meet the definiteness and clarity requirement merely according to the Enforcement Rules of the Patent Act in that the patent specification in question does not specify the corresponding structures, materials or acts. It remains to be seen whether the Intellectual Property Court will adopt a consistent view on matters of this nature.