In a method of manufacturing a semiconductor device, a second wiring substrate is stacked over a first wiring substrate using a conductive paste, where each wiring substrate has mounted thereon an electronic component. The conductive paste is hardened to form a metal column which forms an electrical connection between the first wiring substrate and the second wiring substrate. The wiring substrates are sealed with a resin. The semiconductor device can be downsized, thinned, and made highly reliable, and its manufacturing cost can be reduced. By using conductive paste for the electrical connection between the wiring substrates, a connecting pitch can be smaller than that in a connecting method of using a solder ball including Cu core, and a connection at low temperature can be achieved. Also, by coating the conductive paste by a print-coating or dispense-coating method, manufacturing is simplified and the manufacturing cost is reduced.