The present disclosure relates to a semiconductor device, a solid-state image pickup element, an image pickup device, and an electronic apparatus that are enabled to reduce restrictions on materials and restrictions on device configuration. A CSP imager and a mounting substrate are connected together with a connection portion other than a solder ball. With such a configuration, restrictions on materials and restrictions on device configuration are reduced, which has conventionally occurred because it is limited to a configuration in which solder balls are used for connection. The present disclosure can be applied to image pickup devices.