Shi-yuan Barbie Hsu (Chinese: 徐熙媛; pinyin: Xú Xīyuán; 6 October 1976 – 2 February 2025), also known by her stage name Big S (大S; Dà S), was a Taiwanese actress, singer, and television host. She debuted alongside her younger sister Dee Hsu (Little S) in 1994 as part of the musical duo S.O.S (Sisters of Shiu), which was later rebranded as A.S.O.S (Adult Sisters of Shiu) and transitioned into television hosting. The sisters co-hosted variety shows such as Guess (1996–2000) and 100% Entertainment (1998–2005) before Barbie shifted her focus to acting.

As an actor, Hsu rose to pan-Asian fame with her leading role in the television drama Meteor Garden (2001–2002), which is credited with ushering in the idol drama genre and the golden era of Taiwanese television. She went on to star in dramas such as Mars (2004), Corner with Love (2007), Summer's Desire (2010), as well as in the films Connected (2008) and Reign of Assassins (2010). After her first marriage in 2010, she gradually stepped back from her career.

Hsu ranked 33rd on the Forbes China Celebrity 100 in 2010, 16th in 2011, and 45th in 2012.

Hsu was born on 6 October 1976 to Hsu Chien and "May" Huang Chun-mei in Taipei as the second child of three sisters. She had an elder sister, Hsu Shi-hsien, and a younger sister, Dee Hsu.

Hsu's paternal family owned a jeweler's shop in Taipei, founded by her paternal grandfather, a waishengren from Tancheng County, Shandong, for over 60 years until its closure in 2018. When she was young, her mother, a benshengren originally working as a waitress at the restaurant next to the Hsus' shop before marriage, separated from Hsu's father, the only son with seven sisters, due to pressure from his family to bear a son, along with his infidelity, domestic abuse, alcoholism and gambling. Her mother worked as a real estate broker to support Hsu and her two sisters while her father fled due to his gambling debt when she was 14, though he later returned. Her parents formally divorced in late 2008 as part of an agreement in which Barbie and Dee settled their father's gambling debts one final time—reportedly after he was held hostage by debt-collecting triad members along with his girlfriend—in exchange for his signature on the divorce papers. Over the years, they had already paid more than NT$8 million to cover his debts. Their mother acted as a spokesperson and partial manager throughout their career, while their father, who maintained a good relationship with his daughters after he had given up drinking, died from liver cancer in 2012 at the age of 59.

In 1993, Hsu enrolled at the National Kuo Kuang Academy of Arts, then under Taiwan's Ministry of National Defense, and dropped out after one year due to its military-style discipline. In 1994, she and Dee enrolled at the Taipei Hwa Kang Arts School, a vocational senior high school where she majored in the Drama Department and specialized in Chinese opera kungfu, namely the martial arts and acrobatic techniques used in traditional Chinese opera. At Hwa Kang, the sisters befriended classmates Pace Wu, Aya Liu, and three others, forming a close-knit group known as the "Seven Fairies", named after the characters of Chinese folklore. After four of them entered the entertainment industry, they grew close to three fellow artists—Christine Fan, Mavis Fan, and Makiyo Kawashima—who were later also widely associated with the name "Seven Fairies".

I have seven aunts, and my dad was the only son. When my grandfather was alive, I was a fearless little girl—he was my rock, and I loved him dearly. After he passed, I realized it was my turn to take care of the family. I was lucky to land a commercial acting job at 14, which allowed me to support myself and my loved ones. That's how I became independent. Now that my father is gone, my mom and the three of us sisters take care of one another.

At age 11, Hsu made her first film appearance as an extra in The Sea Plan (1987), directed by Heinrich Wang. At 14, after her sister Dee was scouted while running on the school playground and invited along with their family to audition for a commercial directed by Wayne Peng and featuring singer Chou Chuan-huing, the three Hsu sisters and their mother attended the tryout together. Barbie then began working as a commercial actress, initially and primarily under Peng's direction, to help support the family financially. Her work included a beverage commercial with Takeshi Kaneshiro at age 17, which would also be shown in the film The Ring (2002), prior to her enrollment at Taipei Hwa Kang Arts School.