Melinda Gates made the announcement Monday, writing ... "After careful thought and reflection, I have decided to resign from my role as co-chair of the Bill & Melinda Gates Foundation. My last day of work at the foundation will be June 7th."

She adds, "This is not a decision I came to lightly. I am immensely proud of the work the foundation that Bill and I built together and of the extraordinary work it is doing to address inequities around the world. I care deeply about the foundation team, our partners around the world, and everyone who is touch by its work."

MG goes on to say she's leaving the foundation in good hands -- highlighting CEO Mark Suzman and the board of trustees, among others ... and saying the time to leave is now.

In terms of where she's going to focus her efforts next, Melinda says this ... "This is a critical moment for women and girls in the U.S. and around the world -- and those fighting to protect and advance equality are in urgent need of support."

She says that under the terms of her agreement with Bill, she's walking away with an additional $12.5 billion to commit to new charities and orgs with this emphasis in mind.

Of course, when Melinda divorced Bill a few years ago ... she had a nice golden parachute to go with it -- being afforded tens of billions of dollars after being married to the Microsoft co-founder for 27 years. She's one of the richest women in the world now as a result.

With her exit from the foundation ... she's got even more cash to throw around and spend as she wishes -- and it sounds like she's going to invest in orgs that help and support ladies.

The Bill & Melinda Gates Foundation has been around since 2000, and it's considered the second-largest charitable foundation on earth -- having thrown billions of dollars at a number of causes ... including vaccine development, nutrition and health efforts and education equity.