The solid state imaging device having an array of bit units formed in a semiconductor substrate. Each bit unit is comprised of a phototransistor having a collector formed of the semiconductor substrate an emitter and a base, a switching transistor of the MOS type having a drain connected to the emitter of the phototransistor, an initializing transistor of the MOS type having a drain connected to the base of the phototransistor, a source receptive of a first reference voltage, and a gate connected to the emitter of the phototransistor, and a resetting transistor of the MOS type having a drain connected to the emitter of the phototransistor, a source receptive of a second reference voltage, and a gate receptive of a reset signal. The resetting transistor operates in the reset signal to enable the initializing transistor to initialize the phototransistor. The switching transistor drives the initialized phototransistor to effect reading of image.