This paper presents an experimental study of rarefied gas flow in a trapezoidal microchannel with a constant depth of 103 μm, top width of 1143 μm, bottom width of 998 μm and length of 2 cm. The aim of the study is to verify the upper limit of the validity of the second-order slip boundary condition to model rarefied gas flows. The slip coefficients and the tangential momentum accommodation coefficient (TMAC) are determined for three different gases, viz. argon, nitrogen and oxygen, and it is observed that they compare well to theliterature values. The range of mean Knudsen number (Knm) investigated is 0.007–1.2. The non-dimensional mass flow rate exhibits the well-known Knudsen minimum in the transition regime (Knm ~ 1). It is seen that the Navier–Stokes equation with a second-order boundary condition fits the data satisfactorily with a high value of correlation coefficient (r² >99.95%) in the entire range of Knm investigated. This work contributes by extending the range of Knudsen number studied in the context of validity of the second-order slip boundary condition.