How can i design a professional wordpress theme ?

i searched the net and found nothing but a few softwares like artisteer which is very limited
and u can’t design what u want exactly, it’s a samples nothing more or less, plus i couldn’t
find the full version of the softwares so it’s making watermark on the saved templates.

so, i’m a good photoshop designer, i want to design a wordpress theme

what am i suppose to do ?

thank u & srry for the english
Thank you guys, good answers.

e-commerce web design