AirHint found the following cheapest return flights from Denver (DEN) to San Jose (SJO) in September 2025 (see full year).

Return flights

19 Sep - 26 Sep	American Airlines
23 Sep - 28 Sep	Southwest Airlines
01 Sep - 15 Sep	American Airlines
30 Sep - 05 Oct	Southwest Airlines
22 Sep - 22 Sep	Frontier Airlines
09 Sep - 09 Sep	Frontier Airlines

Also check the deals for one-way flights from Denver to San Jose in September.

The deals are updated regularly. The prices may go up as tickets are purchased by other travellers. Only the cheapest flights are offered. Select a price to book and secure these cheap prices.

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Cheapest return flights from Denver to San Jose in September from $295

Return flights