This paper reports hydrogel mechanical resonators with thin metal film piezoresistors deposited through a hydrogel shadow mask to enable electrical deflection and frequency readouts of resonators. First, circular membrane resonators are simply fabricated by spatially-modulated UV curing of thin polyethyleneglycol diacrylate (PEG-DA) prepolymer on top of polymethylmetacrylate (PMMA) – polydimethylsiloxane (PDMS) composite substrates and dry-state “plugging-out” sacrificial process of the PDMS. Digital micromirror device (DMD)-based dynamic mask lithography is used for spatial modulation of UV light and fabricated hydrogel membrane resonators exhibit diameters of 1 mm and thicknesses of 15 μm. The hydrogel shadow mask is also fabricated with PEG-DA by the dynamic mask lithography. The thickness of the shadow mask is 100 μm and the minimum dimension of the opening is 30 μm. With the hydrogel shadow mask placed over a hydrogel membrane resonator, thin metal (Ti/Au) films, 40 and 80 nm thick, respectively, are deposited by an electron beam evaporator. Then, the deposited thin metal film piezoresistor along with three off-chip resistors makes a Wheatstone bridge that is configured with a differential amplifier. With the constructed readout circuitry, electrical readouts of deflection and frequency of hydrogel membrane resonators are demonstrated and compared with a typical reflection-type optical readout.