Air–water interfaces play an important role in the superhydrophobicity for the surface, which is always made of hydrophobic materials. In the present study, microstructures made of hydrophilic material with different topologies were fabricated on the sidewalls of a microchannel, and the detailed formation processes of air–water interfaces were captured by a microscope and a high-speed camera. The current study found that doubly reentrant structures, even made of wettable material, can capture and sustain the air–water interface. Considering Laplace equation and the geometry restrictions, critical pressure difference in the channel was estimated, and the influences of the structure parameters (the structure spacing and the reentrant angle) were investigated.