A semiconductor detector configured to measure energy of electromagnetic wave on the basis of an electric charge amount of electric charge carriers generated by making incidence of the electromagnetic wave into a depletion layer applied with a drift electric field; wherein the semiconductor detector is configured to move the electric charge carriers and to collect them in a reading electrode by the drift electric field, the semiconductor detector comprising: a first semiconductor chip having the reading electrode and a reading electrode pad electrically connected to the reading electrode formed therein; and a second semiconductor chip having an amplifier electrically connected to the reading electrode pad, the second semiconductor chip being connected to the first semiconductor chip in a flip-chip connection state, wherein an underfill is injected into a gap between the first semiconductor chip and the second semiconductor chip except for a first connection portion connecting the reading electrode pad and the amplifier, wherein the amplifier includes a field effect transistor having a gate electrode, characterized in that the second semiconductor chip has a gate terminal electrically connected to the gate electrode, and the first connection portion is made of a first connection structure connecting the reading electrode pad and the gate terminal through a bump electrode, wherein a first guide portion for use in suppressing the first connection structure from being surrounded by the underfill is formed in the first semiconductor chip, wherein the second semiconductor chip has an output terminal that outputs an amplified signal that is amplified by the amplifier, the first semiconductor chip has an output electrode pad electrically connected to the output terminal, and the underfill is injected into a gap between the first semiconductor chip and the second semiconductor chip except for not only the first connection portion connecting the reading electrode pad and the amplifier but also a second connection portion connecting the output electrode pad and the output terminal, wherein the second connection portion is also surrounded by a space having a lower permittivity than a permittivity of the underfill. a first semiconductor chip having the reading electrode and a reading electrode pad electrically connected to the reading electrode formed therein; and a second semiconductor chip having an amplifier electrically connected to the reading electrode pad, the second semiconductor chip being connected to the first semiconductor chip in a flip-chip connection state, wherein an underfill is injected into a gap between the first semiconductor chip and the second semiconductor chip except for a first connection portion connecting the reading electrode pad and the amplifier, wherein the amplifier includes a field effect transistor having a gate electrode, characterized in that the second semiconductor chip has a gate terminal electrically connected to the gate electrode, and the first connection portion is made of a first connection structure connecting the reading electrode pad and the gate terminal through a bump electrode, wherein a first guide portion for use in suppressing the first connection structure from being surrounded by the underfill is formed in the first semiconductor chip, wherein the second semiconductor chip has an output terminal that outputs an amplified signal that is amplified by the amplifier, the first semiconductor chip has an output electrode pad electrically connected to the output terminal, and the underfill is injected into a gap between the first semiconductor chip and the second semiconductor chip except for not only the first connection portion connecting the reading electrode pad and the amplifier but also a second connection portion connecting the output electrode pad and the output terminal, wherein the second connection portion is also surrounded by a space having a lower permittivity than a permittivity of the underfill.