Siew Wan-chang (Chinese: 蕭萬長; pinyin: Xiāo Wàncháng; Pe̍h-ōe-jī: Siau Bān-tiâng; born 3 January 1939), known also by his English name Vincent Siew, is a Taiwanese politician who served as the ninth vice president of the Republic of China (Taiwan) from 2008 to 2012. He was the first Taiwanese-born premier of the Republic of China and former vice-chairman of the Kuomintang (KMT).

Siew was born in Chiayi on January 3, 1939, during the Japanese rule of Taiwan. After graduating from National Chiayi Senior High School in 1957, he studied diplomacy at National Chengchi University (NCCU) and graduated with a bachelor's degree in 1961. He then completed two years of military service in the Republic of China Armed Forces and passed the Foreign Affairs Special Examination in 1962.

In 1965, Siew earned a master's degree in international law and diplomacy from NCCU. Although he was accepted by Harvard University, Siew chose to remain in Taiwan heeding his mother's wishes. He completed a leadership seminar at Georgetown University in the United States in 1982 and was awarded Eisenhower Fellowships in 1985.

In April 1966, he was appointed as vice consul at the ROC Consulate-General in Kuala Lumpur, Malaysia, and promoted as consul in 1969, a position he held until 1972. During his office term, he built close relationship between Taiwan and the governments and people of Malaysia and Singapore. He also successfully negotiated the establishment of the Trade Mission of the Republic of China in Singapore and its counterpart Singapore Trade Office in Taipei.

After the switch of China seat at the United Nations on 25 October 1971 from Republic of China (ROC) to the People's Republic of China (PRC) and amid massive changes within the international community, Siew determined to return to Taiwan. Once home, he became a section chief at the Department of East Asian and Pacific Affairs of the Ministry of Foreign Affairs (MOFA).

He then joined the Board of Foreign Trade (BOFT) under the MOFA in 1972 which he rose from an inspector, department director until deputy director-general. He used to travel frequently between Taiwan and the United States (US) for bilateral trade agreement negotiation until the US switched diplomatic relations from ROC to PRC on 1 January 1979. In January 1982, he became the director-general of BOFT. During his office term, he worked towards simplifying laws and regulations, and also strengthening personnel management at the BOFT. To reduce the trade surplus between Taiwan and the US, he led trade missions to cover almost all US states as part of a campaign that drew considerable attention. He also participated in a number of additional trade missions to major trading nations to enhance economic and trade relations and resolve trade disputes. He vigorously promoted trade liberalization and globalization. He also authorized banks to process import-export permits, promoted professional training and introduced a rotating system for economic and trade representatives stationed outside Taiwan. His efforts helped build Taiwan's very substantial foreign-exchange reserves and made Taiwan the world's 13th largest trading nation.

As a member of the ruling Kuomintang (KMT), he was named to the Central Committee of KMT in July 1988.

Siew was elected a member of the Legislative Yuan from 1996 to 1997. He was the KMT vice-presidential candidate in 2000 on the ticket of Lien Chan.