An experimental investigation was conducted to study flow boiling heat transfer to n-hexane. Two different test sections were employed: a single 0.3 . 12.7 mm(2) rectangular microchannel and a 0.5 mm concentric annulus of 6 mm inner diameter. Both test sections were electrically heated. The examined parameter ranges were: mass fluxes between 50 and 400 kg/(m(2) s) and heat fluxes up to 106 kW/m(2), at an outlet pressure of 0.1 MPa. Infrared thermography was employed to measure the outer wall temperatures of the rectangular channel and to determine the heat transfer coefficients. This measurement method was especially appropriate for the analysis of the transient behavior of boiling in microchannels, which has been often reported in the literature. In addition, flow visualization was carried out under comparable experimental conditions, using an inner heated circular annulus with a narrow gap.