The university has upped its standard entry offer so that anyone aiming for a science-based degree will need two A*s and an A at A-level or equivalent.
The current offer is one A* and two A grades.
For other subjects, the standard entrance offer will remain A*AA, the university said.
Cambridge insisted that the change was not "raising the bar" for would-be students, as more than nine in 10 (92%) successful science applicants had already scored A*A*A or better at A-level.
In a statement, the institution said: "The university believes that the revised offer gives applicants a clearer indication of the level of attainment realistically required to compete for a place, and to thrive on science courses.
"The university will continue to make non-standard offers where appropriate, based on consideration of relevant contextual data including any extenuating circumstances which may have adversely affected an applicant's academic attainment."
The A* grade was first awarded in the summer of 2010 as part of a bid to distinguish between the best students.
To receive the grade, students must score at least 90% on their papers in the second year of their A-levels and obtain an A overall.
Figures published last summer show that  7.6% of exams were awarded an A* in 2013 compared with 7.9% in 2012.
Cambridge was among the first universities to adopt the A* grade - its standard conditional offer to students in 2010 was A*AA.
Oxford University did not use the A* grade for the first two years, but has used it as an admissions requirement since 2012.
The standard minimum entry requirement for Oxford varies by course - from AAA for history, to A*AA for medicine and A*A*A for mathematics. Most science courses require A*AA.
Students who hope to take up a place on a science degree course at Cambridge University will need to score higher grades in their A-levels from 2015.