In this paper, a periodic array of phototransistors is introduced for CMOS image sensors. Each device comprises a Si nanowire (NW) of varying diameters positioned above a bipolar junction transistor (BJT). The Si NW connects directly to the BJT"s base region. Si NWs with distinct diameters resonate at particular wavelengths, leading to high optical absorption at the distinct regions of the visible light spectrum, namely blue, green, or red. Upon absorption, the photocurrent from the Si NW is injected into the base region, causing the BJT to transition from cutoff to the forward active mode. The amplifying function of the transistor yields superior quantum efficiency, as corroborated by TCAD simulations.