Stargate is a 1981 horizontally scrolling shooter video game developed by Vid Kidz and published by Williams Electronics for arcades. Designed by Eugene Jarvis and Larry DeMar, it is a sequel to Defender , which was released earlier in the year. It was the first of only three productions by Vid Kidz, an independent development house formed by Jarvis and DeMar. Some home ports of Stargate were renamed Defender II for legal reasons.

This sequel adds new ships to the alien fleet, including Firebombers, Yllabian Space Guppies, Dynamos, Phreds, Big Reds, Munchies and Space Hums. The Defender ship is now equipped with an Inviso cloaking device, which renders the ship invulnerable when activated, but has a limited charge. A Stargate transports the ship to any humanoid in trouble. There are two special stages: the Yllabian Dogfight, first appearing at wave 5 and recurring every 10 waves; and the Firebomber Showdown, first appearing at wave 10 and also recurring every 10 waves.

The player flies a small spaceship above a scrolling, mountainous landscape which wraps around, so flying constantly in one direction will eventually return to the starting point. The player's ship flies in front of the landscape and does not contact it.

The terrain is inhabited by a small number of humanoids. Enemy ships fly overhead. The goal is to destroy the enemies to prevent the humans from being captured.

The player is armed with a beam-like weapon which can be fired rapidly in a long horizontal line ahead of the spaceship, and also has a limited supply of smart bombs, which can destroy every enemy on the screen. The player also has a limited supply of "Inviso" cloaking energy, which makes the ship invisible, and able to destroy any ships it comes in contact with.

At the top of the screen is a mini-map, which displays the positions of all aliens and humans on the landscape.

There are fifteen types of aliens:

The game starts with ten Humanoids inhabiting the planet. Landers will attempt to capture and fuse with them during play.