The offer, contained in a letter to Yahoo's board, is 62% above Yahoo's closing share price on Thursday.
Yahoo cut its revenue forecasts earlier this week and said it would have to spend an additional $300m this year trying to revive the company.
It has been struggling in recent years to compete with Google, which has also been a competitor to
"We have great respect for Yahoo, and together we can offer an increasingly exciting set of solutions for consumers, publishers and advertisers while becoming better positioned to compete in the online services market,"
There has not yet been any comment from Yahoo.
Its chief executive, Jerry Yang, announced on Tuesday that he intended to lay off 1,000 staff as part of a restructuring plan.
Terry Semel, who stepped down as chief executive last June, also quit as non-executive chairman on Thursday.
Yahoo shares have fallen 46% since reaching a year-high of $34.08 in October. They rose 54% in pre-market trading.
"Ultimately this corporate marriage was forced by the rise of Google, which has grown into a serious competitor for both
"It is a shotgun marriage, but the person holding the shotgun is Google."
According to its letter to Yahoo,
"A year has gone by, and the competitive situation has not improved,"
But there has been some concern about the price that
"To me, the premium seems exorbitant, for what is a dwindling business," said Tim Smalls from the brokerage firm Execution LLC.
"I personally don't see how the synergies of
Other analysts were more enthusiastic about the offer.
"It is a fantastic offer. It is game on," said Colin Gillis from Canaccord Adams.
"This consolidates the marketplace down to Google versus