** U.S. regional lender Stellar Bancorp's STEL.N shares rise 11.7% to $36.44 in premarket trading after buyout announcement and Q4 results
** Prosperity Banshares PB.N said on Wednesday it would buy rival STEL in $2 bln cash-and-stock deal
** STEL shareholders will receive 0.3803 of PB shares and $11.36 in cash for each STEL shares hald, valuing the co at $39.08 per share
** Valuation represents a 19.8% premium to STEL's last close
** STEL also posts strong Q4 results
** Company reports Q4 net income of $26.15 mln, slightly higher than analysts' average estimate of $26.09 mln - LSEG data
** PB shares down 6.4%
** STEL shares gained 9.1% in 2025, the most in four years
(Reporting by Utkarsh Tushar Hathi)
((utkarshtushar.hathi@thomsonreuters.com))