Check out the companies making headlines after the bell:

AK Steel plummeted more than 8 percent during after-hours trading on Monday, after missing second quarter earnings estimates. The company reported earnings of 18 cents per share, missing Wall Street estimates of 20 cents. Its reported revenues were in line with expectations at $1.75 billion for its second quarter.

Texas Roadhouse plunged more than 11 percent in extended-hours trading after missing second quarter earnings estimates. Wall Street estimated that the restaurant chain would report 67 cents per share in earnings, but the company only reported 62 cents per share for the quarter. The company also missed on its top line, reporting $629.2 million in revenue versus the $634 million expected by analysts.

Allison Transmission Holdings jumped more than 5 percent during extended-hours trading after reporting its second quarter earnings. The Indianapolis-based company beat analysts' estimates of $1.00 per share by earning $1.29 per share. The transmission manufacturer also beat sales expectations, reporting $711 million in revenue versus the $654 million expected.

Sanmina Corporation surged more than 6 percent during the extended session after reporting earnings after the bell before paring gains. The electronics manufacturer reported third quarter revenues of $1.81 billion, beating Wall Street estimates of $1.73 billion. However, the company reported lower-than-expected earnings per share of 55 cents, missing analysts' expectations of 57 cents.

Illumina was up 7 percent in after-hours trading after beating Wall Street revenue expectations for the second quarter. The genetic testing tools company reported $830 million in revenue for the quarter versus the $786.6 million estimated by analysts. Illumina earned $1.43 per share, beating Wall Street expectations of $1.11 per share.