Jessica Alba's got her third bun in the oven ... and she's making sure it gets plenty of sun.

Alba's currently enjoying summer in Hawaii on the heels of news she's having another kid. She's already mom to 2 daughters -- 9-year-old Honor and 5-year-old Haven -- with husband Cash Warren.

There's no doubt that Alba's a MILF and looks incredible in nothing but a bikini and baby bump, although she might want to apply sunscreen more liberally, especially when it comes to her belly.