A plate microchannel heat exchanger (MHX) with isosceles trapezoid-shaped reentrant cavities (ITRCs) in the sidewalls was designed. The flow, heat transfer, and pressure drop characteristics of the MHX were analyzed numerically based on the commercial software FLUENT and compared with a traditional rectangular MHX. The influences of the structural parameters of the ITRCs on the heat transfer performance were investigated. The results indicate that the heat transfer capacities of both MHXs increase first and then weaken with the increase in the flow rate. The heat transfer performance is better for the MHX with ITRCs than for the traditional rectangular MHX and the advantage of the former is more apparent at an increased flow rate. At flow rates greater than 130 ml/min, the pressure drop is lower for the MHX with ITRCs than for the traditional rectangular MHX. The best heat transfer performance is observed at the optimum value of the number or the height of the ITRCs. The heat transfer performance decreases with the increase in the coincidence degree of the ITRCs. The heat transfer performance of the from-dense-to-sparse (FDTS) ITRC distribution exhibits advantages at flow rates lower than 60 ml/min, whereas the performance of the from-sparse-to-dense (FSTD) ITRC distribution is better at greater flow rates.