... 5 National Astronomy and Ionosphere Center, Cornell University, Ithaca, NY 14853, U.S.A. In this paper we present new radio and near-infrared observations of a bright Halpha knot located south-east of the Cepheus OB3 association, near the ionization front that divides the S155 diffuse HII region from the Cepheus B molecular cloud. ... The larger of the small--diameter components is a blister-type compact HII region, still partly bounded by high density molecular gas. ...