Staff from the Gough Group, Beca, Tait companies and Comvita have won 19 per cent of all scholarships awarded.
Overall, application success rate is high - 111 applications have been received since 2010 and 64 scholarships awarded.
Labour Party economic development spokesman David Clark said the success of some companies made the scheme seem like an in-club for a privileged few, which resulted in a trip to Harvard at taxpayers' expense.
"Twenty per cent of the scholarships to just four companies, when there are 500,000 companies in New Zealand, doesn't seem like a programme that is accessible to everybody.
"The Government must try harder to ensure that a wide range of business people are made aware of these scholarships, so that the pool of applicants is broadened."
A spokeswoman for the Ministry of Business, Innovation and Employment (Mbie), the department which runs the scholarships, said each application was judged on its merits.
"Mbie administers the fund and is always keen for more companies to be involved, but it's important to note the scholarships are open to all companies who meet the eligibility criteria," she said.
The scholarships are advertised each year, she said, and Mbie constantly reviews whether marketing is reaching a wide range of companies.
Comvita chief executive Brett Hewlett said three scholarships - awarded in 2011, 2012 and 2013 - had been immensely beneficial to the natural health product company.
Any suggestions the company had been unfairly favoured above others was wrong, he said.
The assessment panel for the scholarships includes New Zealand Trade and Enterprise chief executive Peter Chrisp, the head of Victoria University's management school Sally Davenport, and Wendy Lush, HR and consultant at Wendy Lush Consulting.
Economic Development Minister Steven Joyce said he was always keen for more companies to be involved.