National Semiconductor Corp looks so much healthier these days that Standard & Poor’s Corp says it may upgrade the company’s preferred stock rating, which currently stands at B-plus. The review recognises the company’s improving product mix and rising profitability since late 1991, and also takes into account NatSemi’s strengthened capital structure resulting from the expected conversion of a $125m preferred issue to common shares, the ratings agency said, adding that it will assess the rating potential in light of NatSemi’s developing product profile, its earnings recovery and the effects of the recent preferred stock redemption announcement.