Investors with an interest in Semiconductor - Analog and Mixed stocks have likely encountered both ON Semiconductor Corp. (ON) and NXP Semiconductors (NXPI). But which of these two stocks is more attractive to value investors? We'll need to take a closer look to find out.We have found that the best way to discover great value opportunities is to pair a strong Zacks Rank with a great grade in the Value category of our Style Scores system. The Zacks Rank favors stocks with strong earnings estimate revision trends, and our Style Scores highlight companies with specific traits.Both ON Semiconductor Corp. and NXP Semiconductors have a Zacks Rank of # 2 (Buy) right now. This means that both companies have witnessed positive earnings estimate revisions, so investors should feel comfortable knowing that both of these stocks have an improving earnings outlook. But this is just one piece of the puzzle for value investors.Value investors also try to analyze a wide range of traditional figures and metrics to help determine whether a company is undervalued at its current share price levels.The Value category of the Style Scores system identifies undervalued companies by looking at a number of key metrics. These include the long-favored P/E ratio, P/S ratio, earnings yield, cash flow per share, and a variety of other fundamentals that help us determine a company's fair value.ON currently has a forward P/E ratio of 17.93, while NXPI has a forward P/E of 20.20. We also note that ON has a PEG ratio of 0.33. This metric is used similarly to the famous P/E ratio, but the PEG ratio also takes into account the stock's expected earnings growth rate. NXPI currently has a PEG ratio of 2.02.Another notable valuation metric for ON is its P/B ratio of 5.08. The P/B ratio is used to compare a stock's market value with its book value, which is defined as total assets minus total liabilities. For comparison, NXPI has a P/B of 7.20.Based on these metrics and many more, ON holds a Value grade of B, while NXPI has a Value grade of D.Both ON and NXPI are impressive stocks with solid earnings outlooks, but based on these valuation figures, we feel that ON is the superior value option right now. Breakout Biotech Stocks with Triple-Digit Profit Potential The biotech sector is projected to surge beyond $2.4 trillion by 2028 as scientists develop treatments for thousands of diseases. They’re also finding ways to edit the human genome to literally erase our vulnerability to these diseases. Zacks has just released Century of Biology: 7 Biotech Stocks to Buy Right Now to help investors profit from 7 stocks poised for outperformance. Recommendations from previous editions of this report have produced gains of +205%, +258% and +477%. The stocks in this report could perform even better.See these 7 breakthrough stocks now>>Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report ON Semiconductor Corporation (ON): Free Stock Analysis Report NXP Semiconductors N.V. (NXPI): Free Stock Analysis Report To read this article on Zacks.com click here.