Heterojunction bipolar phototransistors, based on GaAs technology, are widely used in optoelectronic integrated circuits. One of the methods to improve phototransistor performance is applying a delta-doped thin base, which causes both a higher current gain and a better time response. There is a lack of information about this kind of device in the literature. Our work presents the results of computer simulations of AlGaAs/GaAs n-p-n phototransistors, with a bulk-doped and delta-doped base working as two- and threeterminal devices. The characteristics and device parameters obtained clearly show that phototransistors with delta-doped base have higher sensitivity and a better time response compared to the structures with a bulk-doped base. Based on simulation results, we modified the epitaxial phototransistor structure with a double delta-doped base that should improve device performance.