A heatsink for natural convection cooling, said heatsink comprising: a plurality of spaced plate fins projecting from a base with a given height (h), said plate fins having a given length and said plate fins being arranged to occupy a given space, said given space having a bottom side, a top side, a main lateral side connecting said top side and said bottom side, a secondary lateral side connecting said top side and said bottom side, and a tertiary lateral side, said tertiary lateral side opposing said secondary lateral side, and said main lateral side connects said secondary lateral side and said tertiary lateral side, channels for allowing air to flow along said plate fins, the channels being formed between pairs of neighboring plate fins with a bottom of the channels being formed by said base and said channels being open or closed along all or part of their length to said main lateral side, and wherein the channels comprise channels of a first type and a second type, at least one pair of neighboring plate fins forms a channel of said first type that extends between said bottom side and said top side and opening said bottom side to said top side, and at least one pair of neighboring plate fins forms a channel of said second type that extends between said secondary lateral side and said top side and opening said secondary lateral side to said top side, at least one of the plate fins of said plurality of spaced plate fins is a plate fin of a first type that extends lengthwise from said bottom side to said top side, at least one of the plate fins of said plurality spaced plate fins being plate fins of a second type that extends lengthwise from said secondary lateral side into said given space in a direction that includes a component towards said top side, and characterised in that: a portion of the plate fins of both the first type plate fins and the second type plate fins in an upper portion of the heatsink closest to the top side extend parallel with one another in a direction that is preferably substantially perpendicular to said top side. a plurality of spaced plate fins projecting from a base with a given height (h), said plate fins having a given length and said plate fins being arranged to occupy a given space, said given space having a bottom side, a top side, a main lateral side connecting said top side and said bottom side, a secondary lateral side connecting said top side and said bottom side, and a tertiary lateral side, said tertiary lateral side opposing said secondary lateral side, and said main lateral side connects said secondary lateral side and said tertiary lateral side, channels for allowing air to flow along said plate fins, the channels being formed between pairs of neighboring plate fins with a bottom of the channels being formed by said base and said channels being open or closed along all or part of their length to said main lateral side, and wherein the channels comprise channels of a first type and a second type, at least one pair of neighboring plate fins forms a channel of said first type that extends between said bottom side and said top side and opening said bottom side to said top side, and at least one pair of neighboring plate fins forms a channel of said second type that extends between said secondary lateral side and said top side and opening said secondary lateral side to said top side, at least one of the plate fins of said plurality of spaced plate fins is a plate fin of a first type that extends lengthwise from said bottom side to said top side, at least one of the plate fins of said plurality spaced plate fins being plate fins of a second type that extends lengthwise from said secondary lateral side into said given space in a direction that includes a component towards said top side, and characterised in that: a portion of the plate fins of both the first type plate fins and the second type plate fins in an upper portion of the heatsink closest to the top side extend parallel with one another in a direction that is preferably substantially perpendicular to said top side.