The eligibility criteria for doing MS by Research in in USA is as follows:

• Degree of graduation
• A GPA of 3( must not be less than this)
• No age limit
• Based on performance in Bachelor's or Masters degree related entrance exam.
• Proof of English proficiency test.
• GRS score of 290 or above.

Hence , a master's degree is not required, stay assured about this.

University offering courses in USA-

• Harvard University
• Stanford University
• Columbia University
• Cornell University
• University of California.