Line an 8x8 pan with foil and spray with non-stick cooking spray, then set aside.
In a microwave-safe bowl combine semi-sweet chocolate chips and 3/4 cup of sweetened condensed milk. Microwave on high for 1 minute; stir and put back in microwave, stirring every 30 seconds, until completely melted.
Pour chocolate mixture into the prepared pan. Spread it evenly and place in the refrigerator to set.
In a clean, microwave-safe bowl, place white chocolate chips and microwave for 1 minute; stir and put back in microwave, stirring every 30 seconds, until completely melted. Add the pumpkin, spice, and vanilla then stir to completely combine.
Pour the mixture on top of the chocolate layer, gently spread pumpkin mixture evenly over the chocolate layer, then refrigerate for 2 hours or overnight.
Slice fudge with a sharp knife and enjoy. Refrigerate fudge for up to one week.