A method of manufacturing a semiconductor device (1, 1A, 1B) comprising the steps of: (a) providing a lead frame (LF, LF1) including: a first device region having a first chip mounting part having a top surface (DPt) with a first semiconductor chip mounted thereon and a plurality of leads including a first lead arranged in vicinity of the first chip mounting part; a second device region having a second chip mounting part having a top surface (DPt) with a second semiconductor chip mounted thereon and a plurality of leads including a second lead arranged in vicinity of the second chip mounting part and coupled to the first lead, the second device region being arranged adjacent to the first device region; and a sealing body collectively sealing the first device region and the second device region, the lead frame (LF, LF1) having a trench part (LDtr) formed thereon as extending in a first direction so as to communicate with a first lead bottom surface (LDb) of each of the first lead and the second lead extending in the first direction and having a narrower width in a second direction orthogonal to the first direction than a width of the first lead bottom surface (LDb) of each of the first lead and the second lead; (b) forming a cutting part in a coupling part between the first lead and the second lead by cutting a part of the coupling part between the first lead and the second lead from the first lead bottom surface (LDb) side by using a first blade moving in the second direction; (c) after the step of (b), removing a metal waste formed inside the trench part (LDtr); (d) after the step of (c), forming a first metal film by performing a plating method to an exposed part of the first lead and the second lead including the cutting part from the sealing body, wherein a depth of the cutting part is larger than a depth of the trench part (LDtr) in a thickness direction of the first lead; and (e) after the step of (d), separating the first device region and the second device region from each other by cutting a remaining part of the coupling part between the first lead and the second lead from the first lead bottom surface (LDb) side by using a second blade moving in the second direction and having a narrower width than a width of the first blade, wherein, in the step of (e), the remaining part is cut so that the second blade does not contact a first lead side surface (LDs) forming the cutting part so as to be continued to the first lead bottom surface (LDb) of each of the first lead and the second lead. (a) providing a lead frame (LF, LF1) including: a first device region having a first chip mounting part having a top surface (DPt) with a first semiconductor chip mounted thereon and a plurality of leads including a first lead arranged in vicinity of the first chip mounting part; a second device region having a second chip mounting part having a top surface (DPt) with a second semiconductor chip mounted thereon and a plurality of leads including a second lead arranged in vicinity of the second chip mounting part and coupled to the first lead, the second device region being arranged adjacent to the first device region; and a sealing body collectively sealing the first device region and the second device region, the lead frame (LF, LF1) having a trench part (LDtr) formed thereon as extending in a first direction so as to communicate with a first lead bottom surface (LDb) of each of the first lead and the second lead extending in the first direction and having a narrower width in a second direction orthogonal to the first direction than a width of the first lead bottom surface (LDb) of each of the first lead and the second lead; (b) forming a cutting part in a coupling part between the first lead and the second lead by cutting a part of the coupling part between the first lead and the second lead from the first lead bottom surface (LDb) side by using a first blade moving in the second direction; (c) after the step of (b), removing a metal waste formed inside the trench part (LDtr); (d) after the step of (c), forming a first metal film by performing a plating method to an exposed part of the first lead and the second lead including the cutting part from the sealing body, wherein a depth of the cutting part is larger than a depth of the trench part (LDtr) in a thickness direction of the first lead; and (e) after the step of (d), separating the first device region and the second device region from each other by cutting a remaining part of the coupling part between the first lead and the second lead from the first lead bottom surface (LDb) side by using a second blade moving in the second direction and having a narrower width than a width of the first blade,