  We investigate the operation of WSi superconducting nanowire single-photon
detectors (SNSPDs) at 2.5 K, a temperature which is ~ 70 % of the
superconducting transition temperature (TC) of 3.4 K. We demonstrate saturation
of the system detection efficiency at 78 +- 2 % with a jitter of 191 ps. We
find that the jitter at 2.5 K is limited by the noise of the readout, and can
be improved through the use of cryogenic amplifiers. Operation of SNSPDs with
high efficiency at temperatures very close to TC appears to be a unique
property of amorphous WSi.
