Asimov’s Science Fiction is an award winning publisher of science fiction stories. They have won 53 Hugos and 28 Nebula awards. They accept submissions from writers on a continuous basis.
According to their website:
“In general, we’re looking for “character oriented” stories, those in which the characters, rather than the science, provide the main focus for the reader’s interest. Serious, thoughtful, yet accessible fiction will constitute the majority of our purchases, but there’s always room for the humorous as well. SF dominates the fiction published in the magazine, but we also publish borderline fantasy, slipstream, and surreal fiction. No sword & Sorcery, please. Neither are we interested in explicit sex or violence. A good overview would be to consider that all fiction is written to examine or illuminate some aspect of human existence, but that in science fiction the backdrop you work against is the size of the Universe. “
They pay 8-10 cents a word for the first 7,500 words. Which means a payment of up to $750. They pay a flat rate for longer works.
To learn more, be sure to read their submission guidelines.
If you’re looking for an even higher paying speculative fiction market, consider Tor.