Monolithic humidity sensor devices, and methods of manufacture. The devices include circuitry on or over a silicon substrate. A primary passivation barrier is formed over the circuitry with conductive vias therethrough; a capacitor, comprising metal fingers with spaces therebetween, is formed above said primary passivation barrier and electrically coupled by the conductive vias to the circuitry. A secondary passivation barrier is formed over the capacitor. A hygroscopic material layer is formed over the secondary passivation barrier, wherein the capacitor is operable to exhibit a capacitance value responsive to moisture present in the hygroscopic material layer and the circuitry is operable to generate a signal responsive to said capacitance value.