Abstract. Optical crosstalk from a 1.3m laser to a 1.55m photodiode on a single InP substrate, and its suppression within 1.3m/1.5m Y-junction transceiver OEICs, has been analyzed experimentally. The results indicate that the optical crosstalk suppression is limited by the accumulated light in the OEIC substrate coming mainly from the spontaneous emission of the integrated laser and from stray light at the laserwaveguide butt joint interface. For OEICs, integrating lasers and photodetectors, the achievable optical intra-chip crosstalk at present will be in the range of 3040dB at the required small die dimensions.