- AT&T has three days to decide if it wants to change its previous offer, Straight Path said.
- The mysterious bidder is rumored to be Verizon, sources familiar with the matter have told Reuters.
Some of the largest telecom companies in the world really want their hands on Straight Path Communications.
Share prices of the wireless technology company closed more than 23 percent higher, to above $155 on Wednesday. The latest surge came after Straight Path said it received a "superior proposal" from a mystery bidder, topping an offer already on the table from AT&T.
The bidding war for Straight Path began in early April, when AT&T signed a merger agreement to acquire the company for $95.63 per share, representing a total value of $1.6 billion.
At the time, this implied a premium on the stock of 204 percent to Straight Path's closing price of $31.41 on Jan. 11, the day before it announced a settlement with the FCC and that it was considering strategic alternatives.
Toward the end of last month though, Straight Path said it received another unsolicited offer from a "multi-national telecommunications company," of $104.64 per share. The company notified AT&T of the superior deal and said it would pay AT&T a $38 million termination fee, should it accept the higher offer from the mystery bidder.
On Wednesday morning, Straight Path announced that the unidentified bidder has now revised its offer up, to $135.96 per share, reflecting a value of approximately $2.3 billion.
Shares of Straight Path closed Tuesday slightly under $126. The stock is up nearly 588 percent over the past six months and has climbed 331 percent from one month ago.
AT&T now has three days to negotiate its previous offer or outbid what's on the table, Straight Path said.
Verizon Communications, which has acquired AOL and is in the process of buying Yahoo, was considering a buyout offer for Straight Path that would top AT&T's initial bid, sources familiar with the matter told Reuters last month. It is unclear if Verizon is the bidder raising its offer Wednesday.
Verizon and AT&T both declined comment to CNBC.
The wireless spectrum held by Straight Path is expected to play a large role in the latest 5G networks. Both AT&T and its bigger rival, Verizon, have been conducting their own 5G trials.
—Reuters contributed to this report.