Semantic Space Invaders is a computer game in which the gameplay is happening entirely in your perception. Inspired by the classic console game "Space Invaders" from 1978, it plays with the genre stereotype of alien invasion movies and offers a semantic plot twist inspired by John Carpenter´s "They Live". To play, touch-drag or move your mouse to view around, click-drag to move around. (There is no shooting button.) Play at http://www.mariogagliardi.com/spaceinvaders.html The game is a flythrough of a nightly cityscape. An army of unidentified flying objects floats over the city. As you explore the city and enter buildings, it gets more difficult to distinguish invaders and city. Once you realize that the city and the invaders are the same, the initial difference folds onto itself: the invaders are the invaded. A semantic space is a space of meaning formulated by signifiers. In 1978, due to the technical possibilities of the time, space invaders were generated on a screen with only a few pixels. Relying on the interpretative faculties of human perception, the game worked within the space it generated through its symbols and movements. Once a semantic space is opened up to a different one, it can collapse. A case in point is Atari´s game "E.T. the Extra-Terrestrial", one of the first games based on a movie. As there was a counterpart in a different medium, the perceptual difference to the movie left players with a sense of disillusionment. The movie eliminated the less realistic semantic space of the game. Due to advances in computer processing power, movies and games are in the meanwhile both driven by similar CGI technology, making their semantic spaces similar.