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In this article, the optical and electrical properties of NPN InP/InGaAs heterojunction bipolar phototransistor (HPT) are studied by two dimensional semiconductor simulation. The phototransistor is modelled using a numerical method, and the results are presented and discussed. This model is based on heterojunction bipolar transistor (HBT) model with the consideration of the optical beam effect. Responsivity of 12.62 A/W for 1100 nm light is achieved when the thickness of base layer is 50 nm. A good qualitative agreement of the numerical and analytical simulated value of both collector current and responsivity as a function of the wavelength with the existing experimental data was achieved. We present a comparative analysis of our obtained solutions at I B = 5 μA with that simulated at I B = 100 μA and we found that the value of optical power (P opt) giving high injection into a phototransistor at I B = 5 μA is three times higher than that at I B = 10 0 μA. The effects of both the base bias current and the incident optical power on the device performance are investigated. The simulation results, which are presented and compared at low, ideal and high base bias current, show that the highest photocurrent and optical gain are obtained when the base bias current reaches the ideal region. The HPT optical characteristics such as the electrical characteristics of HBT are affected by the high injection effect (Kirk effect). • The NPN InP/InGaAs heterojunction phototransistor (HPT) is numerically simulated with a two dimensional model. • The electrical and optical characteristics of HPT are analyzed and compared with low, ideal and high base bias current. • The results prove that the HPT is more sensitive with the higher base bias current, responsivity of 12.62 A/W is achieved. • For I B = 5 μA, the optical power value which can give high injection is three times higher than this for I B = 100 μA. • The photocurrent shows three variations over base bias current. It varies linearly with optical power in the ideal region. [ABSTRACT FROM AUTHOR]