Herron had been playing in Rookie League ball for the Johnson City Cardinals and has gone 5-1 in his last six starts. The hard-throwing right hander has allowed 11 runs over his last 31.1 innings, including a scoreless streak that reached nearly 16 innings.
Selected in the supplemental first round (46th overall) in the June, 2005 First-Year Player Draft as compensation for the Giants' signing of free agent Mike Matheny. Herron received a $675,000 signing bonus.
In his first season as a pro, Herron made 13 starts for Rookie-level Johnson City, going 0-3 with a 5.62 ERA, allowing 47 hits, striking out 49 and walking 27 in 49-2/3 innings.
In 69.2 innings this season, the former high-school All-America has struck out 54 batters.