A circuit substrate for mounting electronic components includes a metal base layer, an electrically conductive layer having electrically conductive traces, and a composite layer disposed between the metal base layer and the electrically conductive layer. The composite layer includes a polymer matrix and a number of carbon nanotubes embedded in the polymer matrix. The composite layer has a first surface in contact with the metal substrate and an opposite second surface. Each of the carbon nanotubes extends from the first surface to the second surface inclined at an angle of from 80° to 100° relative to the first surface.