We fabricate metal /a-Si/metal thin film switches which incorporate hot-wire chemical vapor deposition (HWCVD) Si layers. A H-diluted gas mixture is used to grow the B-doped, 1000 A hydrogenated amorphous silicon (a-Si:H) layers at approximately 10 Angstrom/s. We compare switching behavior in Cr/a-Si:H(p)/Ag and c-Si(p)/a-Si:H(p)/Ag structures containing p-type hydrogenated amorphous silicon. We observed that the switching is polarity-dependent only in the sample on c-Si(p). Switching to a low-resistance state occurs at 0.4 mA/cm(2) when any of the metal contacts are biased positive. When the c-Si(p) is biased positive holes are injected and no switching occurs even up to 4 A/cm(2). We suggest that the switching requires a blocking metal/a-Si(p) contact, possibly because local electrical breakdown initiates metal filament formation. (C) 2003 Elsevier Science B.V. All rights reserved.