Micro-condenser using the phase separation concept was investigated in this paper. Lined pin fin arrays generate liquid passages and vapor passages alternatively in chip width direction. The decreased Gibbs free energy with gas liquid interface advancing pin fin throat location is the mechanism to induce liquid flow from vapor passages to liquid passages. The decreased energy dissipation due to decreased interfacial area between the two phases accounts for pressure drop reduction. Three micro-condensers were investigated: microchannel condenser (SWM), parallel phase separation condenser (PPS with constant cross sections of fluid passages) and conical phase separation condenser (CPS with varied cross sections of fluid passages). Micro-condensers had identical project condensation surface of 25.0 mm by 3.0 mm. The etched depth was 75 mu m. Water-vapor was the working fluid. Compared with SWM, phase separation condensers increased mass flow rate by 15% at similar pressure drops. PPS condenser enhances heat transfer at moderate or smaller cooling intensity, but deteriorates heat transfer at large condensed liquid flow rate, at which over liquid expansion occurs to flood all pin fin side walls. CPS condenser self-adapts variations of flow rates of the two phases to stabilize vapor liquid interface near pin fin membrane. Pin fin side walls facing vapor passage are covered by thin liquid film to eliminate over liquid expansion. CPS condenser enhances heat transfer over entire operating parameter ranges, increasing condensation heat transfer coefficients by 74% maximally while pressure drops are decreased. CPS condenser has the best performance among the three condensers. (C) 2017 Elsevier Ltd. All rights reserved.