The effects of geometric parameters on the performance of a printed circuit heat exchanger have been analyzed using three-dimensional Reynolds-averaged Navier-Stokes equations. The shear stress transport model is used for accurate prediction of the turbulent flows. The numerical solutions are validated in comparison with the available experimental data, and different lengths of the calculation domain have been tested to determine the optimum length of the domain. The effects of two design parameters, namely, the channel angle and the semi-ellipse aspect ratio of the cold channel, on the heat transfer and friction performance in the cold channel have been evaluated. The results indicate that the effectiveness of the heat exchanger is maximized when the cold channel angle is similar to the hot channel angle.