A current assisted avalanche photodetector (CAAPD) is presented with a large detection window of 40 × 40 μm2, having a small 1-fF avalanche diode in its center. To quickly guide the photogenerated electrons to the center for avalanche multiplication, a drift field with associated majority hole current is applied across the neutral detection volume. This first type of CAAPD is fabricated in a conventional 350-nm CMOS process on a high resistive p− epi-layer. The low diode-junction capacitance can be of interest to integrated receivers. The CAAPD is characterized for its basic functionality, including the effects of lateral detection delay and gain.