We present the fabrication and optimization of new integrated microgiant electrorheological (GER) valves for microflow cytometry. Compared to previous GER valves, new GER valves, consisting of an SU-8 layer, a PDMS membrane, and glass layers, were fabricated by 4-mask microelectromechanical systems technology and two new packaging methods. This design enabled good bonding and fluidic interconnection. The thickness of the PDMS membrane was designed such that the membrane deformation was large enough that the cytometry channel was well sealed. The interfacial stress between the PDMS and the PDMS/SU-8 as a function of vacuum plasma treatment time was investigated in detail. The switching behavior of the GER valves was also analyzed and characterized using fluorescence microscopy.