This article reports the outcome of our recent effort in prediction of gas slip flow through micro-and nanochannels. Slip nitrogen flow through short (length to height ratio of 20) and long (length to height ratio of 2,500) microchannels is analyzed and discussed using the spectral element method and the generalize slip model boundary condition of Karniadakis and Beskok. The well-known curvature in pressure distribution, due to the compressible behavior of the gas flow, is observed. Comparison of numerical results with the experimental and direct simulation Monte Carlo (DSMC) data as well as previous reported numerical results showed that the generalized slip model is able to produce reliable results for both short and long microchannels.