This paper describes interchannel crosstalk in a parallel optical receiver at a data rate of 10 Gb/s and higher. Individual paths of interchannel crosstalk are categorized, and each path is investigated in detail with equivalent model measurements and simulations. At a frequency of 10 GHz, three individual package substrate crosstalk paths and supply and ground rails show a significant coupling level of higher than -22.9 dB. Regarding the quantity of coupled crosstalk, the supply and ground rails make the most significant crosstalk paths within the whole frequency range. In the last part of this paper, effective methods of isolating interchannel crosstalk at a single-channel speed of 10 Gb/s and higher are discussed.