  We announce the discovery of the transiting hot Jupiter WASP-157b in a 3.95-d
orbit around a V = 12.9 G2 main-sequence star. This moderately inflated planet
has a Saturn-like density with a mass of $0.57 \pm 0.10$ M$_{\rm Jup}$ and a
radius of $1.06 \pm 0.05$ R$_{\rm Jup}$. We do not detect any rotational or
phase-curve modulations, nor the secondary eclipse, with conservative
semi-amplitude upper limits of 250 and 20 ppm, respectively.
