Leakage power is a serious problem especially for accerelators which use a large size Processing Element (PE) array. Here, a low power reconfigurable accelerator called Cool Mega Array (CMA) with back-gate bias control (CMA-bb) is implemented and evaluated. In CMA-bb, the back-gate bias of the microcontroller and PE array can be controlled independently. In the idle mode, reverse bias is given to the both parts to suppress the leakage current. When high performance is required, forward bias is used to increase the clock frequency. For simple applications, the operational power can be suppressed by using reverse bias only in the PE array. The real chip is implemented with a 65nm experimental process for low leakage applications. The evaluation results show that the leakage current can be suppressed to 300μA by using the reverse bias. The operational frequency is increased from 39MHz to 50MHz with up to 21% increase of operational power by using the forward bias. For simple applications, 8% to 9.4% of operational power is saved by giving reverse bias only to the PE array.