In this paper, a small signal analysis of a Vertical Cavity Surface Emitting Laser (VCSEL) under the parasitic condition is developed. The analysis is based on the transfer function of the considered device under the parasitic case. The dominant pole approximation scheme is used for the reduction of its characteristic equation. The Convolution Theorem is also applied to get the temporal response. All interesting parameters are outlined. The effect of parasitic cutoff frequency is also analyzed. The results show that when the parasitic cut off frequency is lower than the damping rate, the device behaves like first order low pass filter, while it behaves like second order low pass filter when the parasitic cut off frequency is greater than the damping rate. On the other side, the device operates very fast towards the second order low pass filter and up to a peak power within 1.2 ns if the resonance frequency is increased to 2 GHz, so it can be exploited in very high speed optical systems.