** Shares of AI semiconductor equipment maker Amtech Systems ASYS.O down 8% post-market to $19 on planned equity raise

** Tempe, Arizona-based firm commences stock offering; deal size not disclosed

** Intends to use net offering proceeds to grow its semiconductor packaging and advanced wafer substrate fabrication platforms, for potential M&A, working capital and general corporate purposes

** Titan Capital Partners sole bookrunner

** Co has ~14.6 mln shares outstanding as of May 21, per the prospectus, giving it about $300 mln market cap

** ASYS shares closed down 2.9% at $20.65 on Mon, trimming YTD gain to about 65%