The present work investigates and compares boiling heat transfer and two-phase flow of water in a single shallow uniform-cross-section microchannel and a diverging one with a diverging angle of 0.183°. Both types of microchannel are with a depth of about 20 µm and a mean hydraulic diameter of about 33.3 µm. Experiments are conducted to study the effect of channel geometry on boiling heat transfer in the microchannel. It is found that the slug bubbles tend to grow exponentially in the present shallow microchannels, uniform-cross section or diverging. The results reveal that the diverging microchannel presents better performance in boiling heat transfer than that of the uniform-cross-section one, primarily due to more stable two-phase flow in the diverging microchannel. Empirical correlations based on convective boiling are developed, respectively, for both types of microchannel. For the same mass flow rate, the diverging microchannel presents a higher single-phase flow pressure drop, while the two-phase flow in both types of channel shows approximately the same pressure drop for boiling at the same heat flux.