A method and apparatus for trimming a reference cell in a semiconductor memory device are provided. The method includes generating an internal bias current capable of being trimmed, and trimming the reference cell based on the internal bias current. The semiconductor memory device includes a reference cell in which a reference cell current flows between a drain and a source based on a bias voltage, an internal bias current generator configured to generate an internal bias current capable of being trimmed, and a trimming circuit configured to trim the reference cell based on the internal bias current.