Taj Chahal has thrown himself some great birthday bashes. He has rented limos to take his friends to San Francisco. He’s flown to Vegas.

This year, for his 29th birthday, Chahal decided to do something a bit different: He hosted a surprise party for 300 total strangers – complete with birthday cake and party favors for everyone – at Martha’s Kitchen, a San Jose charity that serves meals to the homeless and working poor.

Most of us consider our birthdays as a time to receive, not to give. So why would this guy celebrate his by feeding the homeless?

It’s all about karma, he says.

“If you are blessed to have the things that you have, then you should share them with others.”

Chahal has indeed been blessed. His family moved from India to San Jose when he was 7. After graduating from Independence High School, he attended San Jose State University until his younger brother, entrepreneurial prodigy Gurbaksh Chahal, started his first company at age 16. Taj, then 19, dropped out to work with him. Last year the Chahal brothers sold their latest start-up, BlueLithium, an advertising technology company, to Yahoo for $300 million.

So Taj decided to take some time off, but he’s not the type to veg out in front of the TV all day. He sat down and made a to-do list:

1. Get in terrific shape.

2. Take flying lessons.

3. Do something really nice for people who need help.

After checking the first two items off the list, he began researching local charities and found a video about Martha’s Kitchen on YouTube.

“I was very impressed with the organization. It’s very lean. They really depend on the volunteers.”

Martha’s Kitchen, which opened in 1981 next to Sacred Heart of Jesus Church on Willow Street, serves more than 100,000 meals a year. Everyone is welcome, no questions asked.

A lot of newly rich valleyites would have written a big check, taken the charitable deduction and headed for the spa. But not this guy. He called Edita Cruz, who runs Martha’s Kitchen.

“I thought he just wanted to volunteer,” Cruz said. “So I showed him around and gave him the usual spiel.”

Then Chahal shared his plan with her:

“He said he wanted to buy dinner for everyone. And he wanted it catered.”

Cruz has seen a lot of volunteers come through her doors over the years, but this was the first time she’d heard an offer like this one.

So on Tuesday, when the regulars arrived, they found the dining room decorated with red tablecloths, balloons and festive place mats. Dinner included ravioli and meat balls, salad, garlic bread and, of course, birthday cake.

The tab came to around $8,000.

Chahal, wearing a black T-shirt, red pants and disposable plastic gloves, walked from table to table, serving juice and accepting thank-yous graciously if a bit self-consciously.

One woman told me she asked him how much money he’d made.

“He smiled and said: ‘Not enough.’ “

Chahal shrugged off the praise, focusing on his work, breaking into a smile only occasionally.

“I really want the people to have an experience they will remember,” he said.

No party is complete without gift bags. On the way out, everyone received a box lunch and a bright colored bag containing a towel, toothbrush and other useful things. The kids each got a toy and some treats.

“This is out of this world,” said Nancy McCary, who has been eating at the Kitchen every week for three years. “I wish Taj the best of luck.”

Chahal confided that the first time he volunteered at the soup kitchen he found it a bit overwhelming. “But you get used to it.”

In a valley filled with young people who have too much money, I wondered if Chahal was trying to guilt his peers into doing something for others. But he shrugged off that notion.

“If someone reads about this and is inspired to do something, that’s awesome. But it should really come from the heart.”

So now that he’s checked his good deed off his to-do list, does he have plans for other charitable ventures?

“In the long term, I want to do something big with philanthropy – scholarships, building schools, that sort of thing,” he said. “You know, when you get closer to the big 3-0 you start thinking a lot about your life.”

In the meantime, he’s already planning a product upgrade for next year’s birthday party.

“I’ll definitely do this again. I’d like to find a way to bring more people in and make it even more special.”

Spoken like a true entrepreneur.