Low-crosstalk 1.3-µm Fabry-Perot laser diode (FP-LD) and photodiode (PD) arrays are developed. The arrays are fabricated on semi-insulating substrates and their anodes and cathodes are separated channel by channel to suppress inter-channel electrical crosstalk at high frequency. Crosstalk of less than -30 dB is achieved between neighboring LDs at 3.125 GHz. This is low enough for BER characteristics observed under asynchronous operation of a 4-channel LD array to be no worse than those under single-channel operation. Excellent uniformity of both LD and PD characteristics, high-temperature operation of the LD array, and low-voltage operation of the PD array are also attained. These arrays are suitable for low-cost high-bit-rate parallel optical communications.