This work deals with a facile "liquid-molding" technology to fabricate PDMS microdevices with complex structured microchannels, the main procedures of which involves: (1) Photo-lithographically fabricating chemical micropatterns of hydrogels on silanized glass substrates to form heterogeneous hydrophilic/hydrophobic surfaces; (2) Fabricating stable 3D surface relief patterns of a liquid via dip-coating the hydrogel patterned substrate in a polar solution; (3) Fabricating PDMS microfluidic devices via a slightly modified replica molding procedure, using a liquid patterned substrate as the molding template. In addition to its simplicity compared to conventional microfabrication methods, this technology produces microchannels with 3D surface topography, which allows for more flexibility in device design and applications. We discuss the main features of the liquid-molding method as well as the structural characteristics of liquid-molded microchannels. We demonstrate the potential application of these "liquid-molded" PDMS (LM-PDMS) devices by designing a cell trapping microdevice that is capable of trapping multiple or individual cells through simple operation procedures.