A surface mount type semiconductor device is disclosed. The semiconductor device has testing lands on a lower surface of a wiring substrate with a semiconductor chip mounted thereon. Lower surface-side lands with solder balls coupled thereto respectively and testing lands with solder balls not coupled thereto are formed on a lower surface of a wiring substrate. To suppress the occurrence of contact imperfection between the testing lands and land contacting contact pins provided in a probe socket, the diameter of each testing land is set larger than the diameter of each lower surface-side land. Even when the wiring substrate is reduced in size, electrical characteristic tests using the testing lands can be done with high accuracy.