While many traders and investors took the summer months to get away and get in some rest and relaxation, the stock market was still hard at work.  During the span between Memorial Day (May 26) and Labor Day (Sept. 1), the large-cap S&P 500 index rose by more than 5 percent and set fresh record highs. That means that those who "sold in May and went away" missed out on a decent summer stock rally.  However, some stocks were harder at work than others, with many staging rallies of more than 20 percent.  Among the S&P 500 stocks that notched the strongest performances were names like Petsmart, which gained 29 percent during the summer season. Shares were helped along by a regulatory disclosure that activist hedge fund Jana Partners became the pet supply retailer's largest shareholder, with a near 10 percent stake. Jana Partners wants to explore ways to extract more value from the company.  Read MoreGet that shopping list ready to buy on the dip  Another star performer continues to be semiconductor giant Intel. Shares rallied more than 30 percent during summer vacation. A good chunk of those gains came on the heels of a bullish second-quarter earnings report that sent shares soaring by 9 percent on July 15. The company also increased its stock buyback authorization by $20 billion.  As for the single best-performing S&P 500 stock during the summer season, that distinction goes to a company that's gained 41 percent during that time frame. More recently the company has been making waves in its attempts to sign NBA all-star Kevin Durant to a mega endorsement deal, but ultimately losing out to larger rival Nike.  Under Armour stock has been a summer sizzler, but not just because of the share price appreciation. The company also signed super model Giselle Bundchen to an endorsement deal to help it sell products catered to women.  The top 10 best-performing S&P 500 stocks between Memorial Day and Labor Day this year are listed below.  Read MoreStocks mostly decline after S&P hits another record
As Wall Street returns back to work, these S&P 500 stocks were busy all summer making big returns in investors' portfolios.