Nanowires represent numerous opportunities for nanoelectronics and sensorics, while metal contact fabrication makes the device development rather challenging. Here, we demonstrate that silicon (Si) nanowires deposited on interdigital metal contacts via simple drop casting exhibit an abrupt increase in conductivity upon exposure to ammonia vapors and aqueous solutions due to adsorption of the analyte species. To reduce the noise of the DC resistance measurements lacking ohmic conductivity, we exploit electronic impedance spectroscopy. The resistive response is found to be dependent on the ammonia content in vapor and liquid matter. The results demonstrate a detection limit of 4 μmol·L^-1(80 ppb), a sensitivity of 0.2% μmol^-1·l (0.01%·ppb^-1), and applicability for the low-concentration detection of up to 400 μmol·L^-1(8 ppm) ammonia in aqueous solutions both directly and indirectly with a response rate of up to 0.43%·s^-1and a recovery rate of 0.31%·s^-1and show selectivity to oxidizing species. Thus, we demonstrate that the use of semiconductor nanowires in adsorption sensorics does not require the fabrication of ohmic contacts and present a simple fabrication protocol perspective for the development of highly sensitive room-temperature multi-environment sensors.