Abstract: An internal/external clock option for built in self test is provided. In one embodiment of the present invention, a clock selection circuit (150) is provided. The clock selection circuit (150) comprises an external clock source (152) and an internal clock source (177). A first multiplexer (164) is provided and has the external clock source (152) and the internal clock source (177) as data inputs and an internal clock selection bit value (B.sub.-- CLKMUXB 176) as a data select input. A second multiplexer (156) having the external clock (152) and the output of the first multiplexer as data inputs and a data select input (BCLK.sub.-- EN) based on whether a self-test mode is activated (BIST.sub.-- EN) and the internal clock selection bit value (B.sub.-- CLKMUXB) is also provided. The external clock source (152) or internal clock source (177) is selected based on the value of the internal clock selection bit value (B.sub.-- CLKMUXB 176) and whether the self test mode is activated (BIST.sub.-- EN).