The iconic director's latest blockbuster is out now, and follows a long history of his own sci-fi movies, including the likes of 1977's Close Encounters of the Third Kind, 1982 classic E.T. the Extra-Terrestrial, and 2005's War of the Worlds.
He told Entertainment Weekly: "I'm telling the story about an area of interest that I have never been able to divest myself of.
"It has been too compelling for me, and has kept me thinking about what's out there, what's been out there, and how come we've not been told it's out there.
"And I wanted to finally make this movie, in a way, as a summation film for all the sci-fi films I've made, starting with Firelight when I was 17 years old on 8mm film - about the truth about are we alone, or are we not alone?"
However, Spielberg has made it clear that despite speculation from fans, his new movie is not a follow-up to his 1977 classic.
"It is not a sequel in any way, shape or form to Close Encounters."
Both films do feature cover-ups of alien activity, although Spielberg pointed out that in Disclosure Day, the government is not hiding them.
He explained: "I really don't believe that governments can keep secrets.
"But big tech companies can. And there are contracting companies that I believe hold all the knowledge and have the archives, not governments."
Disclosure Day stars Emily Blunt as a meteorologist alongside Josh O'Connor as a young cybersecurity expert.
Blunt's character is inadvertently brought into a conspiracy to reveal information about aliens on earth.
The star-studded cast also includes Colin Firth, Eve Hewson and Colman Domingo.
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