Search Engine Marketing SEM, is a form of Internet Marketing that seeks to promote websites by increasing their visibility in the Search Engine results pages (SERPs) and has a proven ROI (Return on Investment). According to the Search Engine Marketing Professionals Organization, SEM methods include: Search Engine Optimization (or SEO), paid placement, and paid inclusion.[1] Other sources, including the New York Times define SEM as the practice of buying paid search listings, different from SEO which seeks to obtain better free search listings.