July 14 (Reuters) - China's Tsinghua Unigroup Ltd offered to buy U.S. memory chipmaker Micron Technology Inc for $23 billion, The Wall Street Journal reported, citing people familiar with the matter.

Tsinghua Unigroup offered $21 per share for Micron, which is at a 19.3 percent premium to the stock's close on Monday, the Journal said. (http://on.wsj.com/1fE2GQm)

Micron was not immediately available to comment on the report.

(Reporting by Sneha Banerjee in Bengaluru; Editing by Stephen Coates)