NEW YORK (CNNMoney) -- Best Buy founder Richard Schulze made a bid Monday to buy the retailer's outstanding shares in a deal that would value the company at more than $8 billion.

Best Buy shares surged 13.3% Monday to close at $19.99. But the stock had jumped about 20% at the start of trading.









Schulze, a former chairman who already owns 20.1% of Best Buy's (BBY, Fortune 500) shares, has offered to buy all outstanding shares for $24 to $26 each, according to a statement.

Schulze owns about 69 million shares, according to an SEC filing from the company. As of May 5 -- the reporting date for Best Buy's first fiscal quarter -- the company had nearly 343 million diluted shares, including Schulze's outstanding.

The founder said he plans to use about $1 billion on his own money in conjunction with investments from private equity firms to raise the capital, with the help of financial adviser Credit Suisse (CS). He is also trying to get former chief executive officer Brad Anderson and former president and chief operating officer Allen Lenzmeier to rejoin the company.

However, Standard & Poor's has already taken a skeptical view of the proposed deal. S&P downgraded Best Buy's credit rating to junk status Monday.

"The transaction, if completed, would materially weaken Best Buy's credit protection metrics because we believe it will add a significant amount of debt," said Standard & Poor's credit analyst Jayne Ross.

Ross added that depending on the amount of debt used and the turnaround plan proposed for the company, S&P may eventually cut Best Buy's credit ratting several more notches.

Best Buy has had its fair share of problems as its bricks-and-mortar stores struggle to compete with online retailers including Amazon (AMZN, Fortune 500), Apple (AAPL, Fortune 500) and RadioShack (RSH), and announced back in March that it was closing 50 stores in the U.S.

Schulze stepped down as chairman in June after he was caught up in a scandal with the former CEO Brian Dunn. The company said that Dunn violated company policy by engaging in an inappropriate relationship with a female coworker.

Best Buy's board of directors said that Schulze "acted inappropriately" by not telling the board's audit committee about Dunn's relationship with the employee back in December, when he found about it.

At the time, Schulze said, "I understand and accept the findings of the Audit Committee."

Schulze had been with the company since he launched it in 1966.