The issue of entropy generation in laminar forced convection of a Newtonian fluid through a slit microchannel is analytically investigated by taking the viscous dissipation effect, the slip velocity and the temperature jump at the wall into account. Flow is considered to be hydrodynamically fully developed but thermally developing. The energy equation is solved by means of integral transform. The results demonstrate that to increase Knudsen number is to decrease entropy generation, while the effect of increasing values of Brinkman number and the group parameter is to increase entropy generation. Also it is disclosed that in the thermal entrance region the average entropy generation number over the cross section of channel is an increasing function of axial coordinate.